As wireless technologies proliferate, mobile wireless devices incorporate a multiplicity of different wireless standards. For example, a cellular telephone can accommodate a cellular network (e.g., Universal Mobile Telecommunications System), a wireless local area network (“WLAN”), such as IEEE 802.11, and a wireless personal area network (“WPAN”) such as Bluetooth (BT). Including WPAN access makes utilization of a wireless device more convenient by allowing use of wireless headsets and other short-range wireless appliances.
Some wireless networks occupy an adjacent or overlapping frequency spectrum. For example, BT and IEEE 802.11b/g/n, and WiMax can utilize the same 2.4-2.5 GHz band. Mobile wireless devices are sometimes capable of accessing multiple wireless networks, such as a cellular smart phone that supports radios in overlapping RF bands (a combination device that is referred to herein as a “combo device”).
Therefore, interference between these technologies operating in the same device creates challenges on the coexistence of these two wireless interfaces. More specifically, the out of band emission by either technology may saturate the receiver of the other technology and hence, blocking may occur. The limited medium time available to each radio is more problematic.
To solve the network coexistence problem in which WLAN is one of the subsystems operating in the same combo device, time multiplexed operation is used. For example, in the case of WLAN and BT coexistence, BT voice calls can take priority over other traffic flows in WLAN. During the time periods that the combo device operates in BT mode, the WLAN can operate in unscheduled automatic power saving delivery (U-APSD) mode. During the time that the combo device operates in WLAN mode, it sends a trigger frame (or a PS-Poll if legacy power save mode is used) to the access point (AP) indicating that it is ready to receive packets.
Regarding legacy PS mode, usually, the node/station (node/STA) tries to send the PS-Poll frames immediately after the BT active gap is over, therefore increasing the chances that the AP will send a data frame during the BT idle gap. However, depending on how congested the network is, the AP may not be able to send the data frame during the BT active gap. Hence, the node/STA sends the clear to send (CTS2Self) frame to protect from the avalanche effect. However, as described below, for long aggregated packets such as aggregated medium access control (MAC) protocol data unit (A-MPDU) packets, CTS2Self may become unreliable.
IEEE 802.11n technology can further complicate coexistence of WLAN and BT technology on combo devices. IEEE 802.11n allows multiple medium access control (MAC) data frames to be carried in a single physical frame (referred to as aggregation or an aggregate). There are two forms of frame aggregation: Aggregated MAC Protocol Data Unit (A-MPDU) and Aggregated MAC Service Data Unit (A-MSDU). These aggregated packets comprising a plurality of data frames have a larger size and occupy (for the most part) a longer duration of time as compared to a single packet transmitted using IEEE 802.11g technology. Performance of IEEE 802.11n with BT voice can degrade substantially, and can result in the combo device being disconnected from the AP.
For example FIG. 1A depicts a known wireless network 100 including an AP for a first network shown as a WLAN AP 110 (hereafter AP), and a combo device 120 identified as a STA1-BT master at a combo node. Combo device 120 communicates over a second network that overlaps the first network shown as BT to a BT slave 125 (e.g., an earpiece), and combo device 120 communicates over WLAN to AP 110. Network 100 also includes several WLAN STAs shown as STA2 (122) and STA3 (123).
FIG. 1B is a timing diagram that depicts activity of the combo device 120 shown as STA1, and AP 110, including the mode that is active as a function of time, showing overlapping of A-MPDU packet transmission from AP 110 intended for receipt by combo device 120 into a BT active interval for combo device 120. A-MPDU packets comprise a plurality of medium access control layer (MAC) frames. Overlap can occur because the transmission of a long A-MPDU by the AP 110 started before a CTS2Self frame is transmitted by the combo device 120, or because the combo device 120 may want to transmit an A-MPDU packet in the uplink (e.g., to AP (110)). SIFS shown stands for short interframe spacing.
Since the transmission of a block acknowledgement (BA) response expected from the combo device to the A-MPDU packet falls within the BT activity interval of the combo device 120, a BA response cannot be transmitted by the combo device 120. The AP 110 will thus not receive an acknowledgement from the combo device 120 and will therefore assume that the A-MPDU packet that was transmitted to the combo device 120 was not received (lost). AP 110 will try to retransmit the same A-MPDU packet at a later time to combo device 110 which reduces the transmission rate and in some instances can result in dropped data.